The present invention relates generally to road milling and trenching machines and more particularly to apparatus for preventing wear on the face of blocks or holders that are used for retaining cutting bits on such road milling, trenching and other machines.
Conventional road milling and trenching machines utilize cutting bits mounted in cutting systems that in normal operations move with respect to a work surface. The cutting systems typically include a plurality of cutting bit holders or blocks that include a bore. Each of the cutting bits includes a cutting surface located at a forward or distal end of the cutting bit that is intended to contact the work surface to mill or mine material from the work surface. Each of the cutting bits also includes a shank located at a rearward or proximal end of the cutting bit that is received in a bore in a cutting bit holder or block.
During use, impacts between the cutting bits and the work surface cause the cutting bits to rotate with respect to the holder. The impact induced rotation also causes relative movement between confronting surfaces of the cutting bit and holder. The environment in which such machines are typically operated generally includes abrasive particulate materials that are displaced from the work surface and can be entrained between the confronting surfaces of the cutting bit and holder. The relative movement in the presence of the abrasive particulate materials causes significant frictional wear that can result in a variety of failure modes for the cutting system.
Attempts have been made to focus the wear on cutting system elements that are easily replaced, such as the cutting bits, rather than on the system elements that are more or less permanent portions of the cutting system, such as the cutting bit holders. For example, the cutting bit shank is typically rotatably mounted within a sleeve that is received within the bore of the cutting bit holder. Preferable the sleeve is sized so that it tightly grips or engages the bore of the cutting bit holder and does not rotate with respect to the holder. In this way, the frictional wear occurs on the confronting surfaces of the sleeve and bit shank, both of which are easily replaced. The conventional sleeves do nothing to protect other confronting surfaces of the cutting bit and bit holder. As a result, excessive wear occurs on the face of the cutting bit holder or block into which the cutting bit shank extends. After prolonged use, the wear on the face of the holder or block can become severe enough to require its replacement.
Several attempts have been made to alleviate this problem. Beebe, U.S. Pat. No. 4,561,698, discloses a sleeve and wear protector including an annular flange manufactured as a unitary wear protector. The unitary wear protector is manufactured of materials such that it wears at a rate substantially coincident with the wear rate of the cutting bit. However, the unitary wear protector may rotate within the bore, thus leading to uneven wear of the protector assembly and wear of the holder or block. Dziak, U.S. Pat. No. 4,489,986, discloses refers to a retainer element mounted on a cylindrical shank of a cutter bit. The cutter bit is mounted within a bore of a holder or block member. The holder or block member includes a cylindrical outer portion including a groove in which is mounted a rubber or plastic ring. The ring is received in another groove within a wear collar that contacts the cutter bit. The rubber or plastic ring further is symmetric about the axis of the cutter bit, and no means is provided to inhibit relative rotation between the collar and the holder or block member. Mercier et al., U.S. Pat. No. 6,113,195, discloses a washer disposed between the holder and the cutting bit that is conical (Belleville) so that the washer makes annular line contact with a shoulder of the cutting bit, and with an edge of the bore of the holder, in order to effectively seal out abrasive fines from the bore and thereby reduce the unwanted wear. No provision is made to inhibit rotation of the washer of Mercier et al, thus resulting in significant wear of the holder surface facing the washer.
O""Neill, U.S. Pat. No. 5,106,166, discloses a unitary sleeve that has a bore for rotatably receiving a cutting bit. The sleeve and holder or block are constructed such that the angular position of the sleeve can be fixed relative to the axis of the aperture in the sleeve in any one of a plurality of discrete positions. The sleeve and holder are constructed such that the sleeve can later be rotated with respect to the axis of the aperture in the holder or block to another position and then fixed in that position. While the construction of O""Neill prevents unwanted wear of the forward facing surface of the block or holder, it requires that the block or holder have specific features not commonly present on most blocks or holders in general use. Thus, the unitary sleeve of O""Neill is cannot be used to reduce the wear of most blocks or holders in general use today. Britzke et al, U.S. Pat. No. 5,931,542, discloses a substantially circular wear washer with a radially inwardly directed key which is adapted to fit within a slot in a sleeve surrounding the shank of the cutting bit, thereby interlocking the sleeve and the wear washer. The holder or block bore includes a keyway which is engaged a radially outwardly directed key on the sleeve thereby interlocking the retainer sleeve and wear washer with the holder or block. In the absence of such a keyway on the interior bore of the holder or block, the sleeve and washer are free to rotate. Thus Britzke et al, like O""Neill, requires that the block or holder have specific features not commonly present on most blocks or holders in general use.
What is needed is a wear washer, which is adaptable for use on a wide variety of existing holder or blocks that will inhibit or prevent wear of the forward facing surface of the holder or block. Preferably the wear washer can be coupled to a wide variety of conventional cutter bits so that it can be replaced with each replacement of the cutter bit.
Accordingly, a cutter tool has a tool holder and a cutting bit as well as a washer of the present invention. The tool holder includes a holder surface having a bore extending rearward through the holder surface and an outer edge spaced from the bore. The cutting bit includes a body having a front cutting tip, a rearward projecting shank rotatably mounted in the bore of the tool holder, and a rearward facing bit shoulder disposed at a front end of the shank. The shank is rotationally symmetric about a longitudinal axis of the cutting bit. The washer is disposed between the bit shoulder and the holder surface. The washer comprises a front surface in sliding engagement with the bit shoulder, and a back surface contacting the holder surface. The back surface includes an axially asymmetric lip engaging the holder surface outer edge so as to inhibit rotation of the washer relative to the holder surface.
The cutting bit and washer can be assembled together to form a cutter assembly of the present invention. The washer includes an inner edge defining a central hole receiving the cutting bit shank. The washer also includes a front surface and a back surface joined by an outer edge of angularly variable radius. The front surface includes at least a portion for sliding contact with the rearward facing bit shoulder. The back surface includes a lip extending rearward from only a segment of the asymmetric edge for engaging an outer shoulder of a holder. The lip can be a linear rearward extension along an outer edge of the back surface of the washer. Where the washer outer edge is in the form of an ellipse, the lip can also be positioned on the back surface of the washer on a major axis of the ellipse. A sleeve surrounding the cutting bit shank includes a forward edge positioned to confront the back surface of the washer adjacent the inner edge for retaining the washer on the cutting bit adjacent to the rearward facing bit shoulder. The washer central hole includes a smooth inner surface that facilitates rotation of the cutting bit relative to the washer.
The portion of the washer in sliding contact with the rearward facing bit shoulder is generally a circular ring portion. In one embodiment, the washer front surface includes an outer tapered portion tapering away from the circular ring portion. In another embodiment, the washer front surface also includes an inner tapered portion, and both tapered portions taper away from the circular line portion in sliding contact with the rearward facing bit shoulder. The outwardly tapered surface tends to inhibit particulate abrasive material from penetrating passed the circular ring contact portion, and thus concentrates any frictional wear into a circular pattern on the rearward facing bit shoulder and the forward facing surface of the washer. Thus, the tool holder forward surface and the tool holder bore experience reduced wear, which contributes to enhanced usable life for the tool holder and more reliable positioning of the cutting bit in relation to the work surface.